The present invention relates to a procedure as defined in the preamble of claim 1.
The invention applies to a wireless local loop (WLL) in which subscriber""s stations are connected via a radio link over a base transceiver station to an access node (AN) and from the access node to a local exchange over a standard V5 interface, in which the subscriber ports are identified by means of an L3 address.
In a GSM-based mobile network (GSM, Global System for Mobile Communications), it is possible to make a so-called emergency call even if the subscriber cannot be identified in the service network concerned (emergency setup). An emergency call can also be made from a mobile station containing no subscriber identification module (SIM). Subscribers connected to a local exchange via a V5 interface consistent with the ETS 300 347-1 standard are identified by their L3 address both in the local exchange and in the access node. The L3 address is an individual number for the subscriber port in the V5 interface. L3 address (Layer 3 address) refers to a layer 3 address according to the OSI model (Open Systems Interconnection).
When a subscriber in a GSM network cannot be served by his/her own network but is within the coverage area of a base transceiver station linked to a GSM based WLL access node, or if the subscriber is in his/her proper network but the subscriber identification module SIM fails, preventing the use of TMSI (Temporary Mobile Subscriber Identity) or IMSI (International Mobile Subscriber Identity) data for call setup, it is possible that the person will try to call a common emergency number if there is an emergency situation. The call will founder on the L3 address because the calling subscriber cannot be identified in the subscriber identification procedure, or authentication procedure, and the subscriber therefore has no L3 address available.
In a prior-art procedure, successful setup of an emergency call is ensured by defining non-existent extra subscribers in the local exchange and access node. In a situation where an unidentified subscriber is trying to call a common emergency number, the call is set up over a V5 interface using the identification data of a non-existent subscriber.
A problem with this prior-art procedure is that it increases the size of the subscriber database.
The object of the invention is to eliminate the above-mentioned drawback.
A specific object of the invention is to disclose a procedure that enables a call originated by an unidentified and/or undefined subscriber in a mobile network to be set up over a V5 interface without the need to create non-existent subscribers in the local exchange.
The procedure of the invention is characterised by what is presented in claim 1.
According to the invention, an emergency call to a predetermined emergency number attempted by a subscriber unidentified and/or undefined in the local exchange is detected during an emergency call and subscriber identification procedure, and a free L3 address is selected and the unidentified subscriber""s emergency call is set up using this free L3 address over a V5 interface in accordance with the ordinary call setup procedure.
In an embodiment of the procedure, the free L3 address is a normal L3 address of an existing subscriber.
In an embodiment of the procedure, the free L3 address is a predetermined value in the V5/L3 address range, and this value has been reserved for the setup of emergency calls, to be used for emergency calls made by unidentified subscribers.